Berkshire Hathaway is loading up on this energy stock.According to the latest 13F filings, Warren Buffett's holding company Berkshire Hathaway (NYSE: BRK.A)(NYSE: BRK.B) increased its stake in just two companies. One of those companies is insurance operator Chubb Ltd. The other is an energy giant that, quite frankly, Buffett is obsessed with. He's a big fan of how the company is being run. After reviewing the company's annual report, Buffett told CNBC: "I read every word, and...this is exactly what I would ...